Nonlinear Numerical Simulation Of Wave-Current Interaction With A Submerged Obstacle

Submerged obstacles are extensively applied in practical engineering, such as submerged breakwaters, submarine oil and gas pipelines. They can be also considered as simplified representations of shallow reefs, sunken rocks, etc. As waves propagating over an immersed obstacle, they undergo strong nonlinear deformations due to nonlinear shoaling effects. Consequently, a number of superharmonic waves are introduced to the flow, which are released as free waves when entering the deep water. Because of the structure’s actions, the wave spectrum is considerably modified, since a portion of energy is transferred from primary wave to higher harmonics. The generation of higher free and bound waves and the modification of wave characteristics will do harm to sailing conditions, coastal structures and coastlines, etc. In coastal zones, waves and currents generally coexist, and currents can significantly affect wave field. Therefore, there is important engineering significance to investigate wave-current interaction with a submerged obstacle.To simulate the interactions between regular waves and an immersed structure in the presence of a uniform current, a2-D time-domain fully nonlinear numerical wave flume is developed by using a higher-order boundary element method (HOBEM). The fluid particles of the instantaneous free surface are tracked by the mixed Eulerian-Lagrangian approach. As a time-marching scheme, the fourth-order Runge-Kutta technique is employed to update the free-surface elevation and the velocity potential on the free surface at next time step. A two-point method and a four-point method are both used to decompose free and bound waves upstream and downstream the structure and for cross-checking.Firstly, we simulate wave-current interaction with a submerged horizontal cylinder. In the presence of a uniform current, the effects of different parameters, such as incident wave amplitude, current velocity, immersion, radius of the cylinder and wave period, on the harmonic amplitudes are considered. Secondly, current effects on wave nonlinear scattering by a submerged plate are investigated, and we focus on current effects on the fundamental wave and the second free wave. The above computed results are in comparison with the published experimental and numerical data to validate the present model. Finally, we analyze the forces and moments exerted on a submerged horizontal plate, the results show that a current affects the forces and moments exerted on a submerged horizontal plate by changing the wave amplitude, the relative wave frequency and the contribution of the term U(?)φ/(?)x in the Bernoulli equation.